Adhesive interactions between myeloma (MM) cells and cells in the marrow microenvironment play an important role in tumor cell homing, lodgment and growth, as well as the bone destructive process in MM. Gene expression profiling of MM cells has shown that annexin II (AXII) is highly expressed by MM cells. We have recently cloned the AXII receptor (AXIIR) and found that AXIIR is also expressed by primary MM cells and MM cell lines. Our preliminary results suggest that AXII/AXIIR interactions play an important role in MM as well as prostate cancer bone metastasis and normal hematopoiesis. The primary goals of this application are to determine the biologic effects of AXII/AXIIR interactions between MM cells and the marrow microenvironment on MM cell growth, adhesion of MM cells to stromal cells and osteoclast (OCL) formation as well as the effects of OCL-derived AXII on MM cells and OCLs. It is our hypothesis that interactions between AXII on stromal cells and AXIIR on MM cells play an important role in lodgment of MM cells in the marrow, growth of MM cells and OCL formation. Further, OCL-derived AXII combined with growth factors released from the bone matrix by the bone destructive process stimulate the growth of MM cells to expand tumor burden in bone. To test this hypothesis: 1) we will determine if MM cells specifically bind AXII via AXIIR;2) determine the contribution of AXII/AXIIR to adhesion and growth of MM cells in the bone marrow microenvironment, as well as the contribution of AXII/AXIIR signaling on expression of key cytokines and adhesion molecules by MM cells and stromal cells. In addition, we will assess the contribution of endogenous stromal cell AXII/AXIIR and MM cell AXII/AXIIR on the growth and adhesion of MM cells;3) we will determine the contribution of OCL-derived AXII on the growth of MM cells;and 4) the role that AXII/AXIIR plays in MM cell homing, lodgment, and mobilization in the marrow in vivo. Results of these studies should determine the potential utility of AXII/AXIIR as a novel therapeutic target for patients with MM. PUBLIC HEALTH RELEVANCE: The primary goals of this application are to determine the biologic effects of AXII/AXIIR interactions between myeloma (MM) cells and the marrow microenvironment on MM cell growth, adhesion of MM cells to stromal cells and osteoclast (OCL) formation as well as the effects of OCL-derived AXII on MM cells and OCLs.